1. Field of the Invention
The disclosure pertains to fouling mitigation in equipment used during hydrocarbon production. In particular, the disclosure pertains to compositions useful for the mitigation of oil, hydrocarbon, silt, insoluble organics, and precipitated inorganic minerals fouling in equipment used during hydrocarbon production, such as heat exchangers.
2. Description of the Related Art
When crude oil or bituminous sands are located sufficiently below the surface of the earth, oil wells can be drilled to assist in the extraction of these materials. However, heavy hydrocarbons can prove difficult to recover or produce due to their high viscosities. Various extraction, recovery, or production methods are known in the art such as flooding the formation with heated water or steam in an attempt to reduce the viscosity of the hydrocarbons to enable flow and aid in production.
One such method known as Cyclic Steam Simulation or the “huff-and-puff” method involves stages of injecting high pressure steam, soaking the formation, and production. The initial stage involves steam injection for a period of weeks to months to heat the hydrocarbon, bitumen or heavy oil resource in the reservoir, thereby reducing its viscosity such that it will be able to flow. Following injection, the steam is allowed to soak in the formation for a period of days to weeks to allow heat to further penetrate the formation. The heavy oil, sufficiently reduced in viscosity, is then produced from the same well until production begins to decline upon which time the three step cycle is repeated. This method requires large amounts of water and the water is generally recycled or reused throughout the process.
Another recovery or production method used in the art is referred to as steam assisted gravity drainage (SAGD). The SAGD recovery method relies on two parallel, horizontal wells approximately 1 km in length. An upper “injector well” resides above a lower “producing well.” The producing well is situated as close as possible to the bottom of the reservoir. Initially, steam is injected into both wells to begin heating the formation. After a period of time, the formation is sufficiently heated such that the viscosity of the hydrocarbons or bitumen is reduced and the hydrocarbons or bitumen are now able to enter the production well. Once this occurs, steam injection into the production well is ceased.
Low pressure steam is continuously injected into the injector well, resulting in the formation of a steam chamber, which extends laterally and above as the process continues. At the edge of the steam chamber, the steam releases its latent heat into the formation. This process heats the hydrocarbons and/or bitumen causing it to be sufficiently reduced in viscosity to drain along the edge of the steam chamber under the influence of gravity to the lower producing well. It can then be pumped to the surface along with the resultant steam condensate. At that point, the formed water and bitumen emulsion is broken and sent to a separation vessel for separation of the hydrocarbons and water.
In addition to imparting a viscosity reduction on the hydrocarbons and/or bitumen, the steam condenses and a hydrocarbon-in-water emulsion forms allowing the hydrocarbon to travel more readily to the producing well. SAGD processes typically recover about 55% of the original hydrocarbon or bitumen-in-place over the lifetime of the well.
The SAGD process relies on the energy intensive production of steam to assist with bitumen recovery. It requires natural gas, significant amounts of fresh water, and water recycling plants.
As can be seen, in the hydrocarbon production industry, large amounts of water can be necessary for the successful recovery or production of various hydrocarbons. Generally, the water is recycled or reused throughout production. Over time, recycled or reused water can become contaminated with silt, sand, clay, hydrocarbons, oil, grease, and other organic materials. As this contaminated water is recycled through the various pieces of equipment used in connection with hydrocarbon recovery, the various pieces of equipment can become contaminated or fouled.
In certain circumstances, the hydrocarbon being produced from a well can be in the form of an oil in water emulsion. The emulsion can then be broken and transferred to a separation vessel. Although most of the hydrocarbons are separated from the water in the separation vessel, the water leaving the separation vessel can still contain certain impurities. This water is subsequently sent to a heat exchanger, and possibly other components, where it can be heated and sent back into the well for further use in production. Since the water cannot be perfectly purified in the separation vessel, it can still contain certain impurities, such as silt, sand, clay, hydrocarbons, and other organic materials. These impurities are carried with the water into the heat exchanger or other components of the system and the impurities can cause fouling of the various pieces of equipment.
For example, as the impure water passes through the heat exchanger, heavy tar-like deposits can accumulate on both the shell side and tube side of the heat exchangers. If the recycled water passing through the heat exchanger has a high concentration of impurities, heavy fouling can occur. In certain situations, the fouling can comprise from about 20-60% sand and clay, from about 20-40% hydrocarbon (such as bitumen), and 10-50% insoluble organics, such as polar organics or organic salts, which could be a combination of naphthenates and demulsifier chemicals, such as esters and oxylakylates. Fouling of the heat exchangers can be very detrimental to the entire operation and can significantly limit and even stop production. For example, from the beginning of the production or recovery process, it could take as little as two weeks for the heat exchanger to become significantly fouled such that it will need to be taken off-line and cleaned, and while it is being cleaned, production or recovery will come to a halt.
Currently, the industry deals with this problem by allowing the heat exchanger to become fouled to the point where either the flow of water is heavily restricted or no effective heat transfer is occurring between the water and the heat exchanger. At that point, the system is stopped and the exchanger is cleaned using certain chemicals and hydroblasting. Since the system must be stopped to clean the exchanger, hydrocarbon recovery or production is significantly reduced over time.
To allow production to continue while the heat exchanger is being cleaned, some sites have a second heat exchanger on standby and when the original heat exchanger accumulates a high degree of fouling, the heat exchanger is taken off-line and the second heat exchanger is substituted therefor. While the second heat exchanger is on-line or in operation, the fouling in the original heat exchanger is cleaned and then this heat exchanger is placed on standby and substituted back into the process once the second heat exchanger accumulates a high degree of fouling. Although this can be a possible solution to the fouling problem, it requires a large amount of labor to manually clean out the fouled heat exchanger and it also requires a large amount of capital as at least two heat exchangers will need to be purchased. Thus, a different solution to the problem of fouling in heat exchangers is desirable.